Two-way electric pulse communication system



Aug. 28, 1951 c. T. scULLY TWO-WAY ELECTRIC PULSE COMMUNICATION SYSTEM Filed Nov. 13, 1948 5 Sheets-Sheet 1 ATTORNEY Aug. 28, 1951 c. T. scuLLY 2,565,525

TWO-WAY ELECTRIC PULSE COMMUNICATION SYSTEM Filed Nov. 15, 1948 5 sheets-s'heet 2 for 2E //4 OT Delay of 74E 822' 75E as l;

9 E 3 EN TOR. CHA/nfs THOMAS 5cl/uy BVMW' A T TOF/VE Y Aug. 28, 1951 c. T. SCULLY 2,565,525

TWO-WAY ELECTRIC PULSE COMMUNICATION SYSTEM Filed NOV. 13, 1948 5 SheebS-Sheel'l 5 G3. L l

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@fd/dw ATTORNEY' Aug. 28, 1951 c. T. SCULLY Two-WAY ELECTRIC PULSE COMMUNICATION SYSTEM 5 Sheets-Sheet 4 .llt

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ATTORNEY Patented Aug. 28, 1951 TWO-WAY ELECTRIC PULSE COMMUN- CATION SYSTERI Charles Thomas Scully, London, England, assignor to International Standard Electric Corporation, New York, N. Y., a. corporation of Delaware Application November 13, 1948, serial No. 59,957 In Great Britain November 26, 1947 13 Claims.

The present invention relates to two-way repeaters for electric pulses, suitable for cases in which the pulses are transmitted in both directions over the same communication medium.

When a common medium such as a cable circuit, or a radio system employing a single carrier frequency, is used for both directions of transmission between the repeater and an adjacent station, it has hitherto been necessary to time the transmitted and received pulses sothat at any station on route, they occur at different times. This imposes retrictions on the repetition frequencies of the pulse trains operating in the two directions, and on the spacing of the stations.

The object of the present invention is to provide a repeater through which pulse trains can be passed simultaneously in opposite directions without imposing any such restrictions.

This object is achieved according to the invention by providing a plurality of parallel paths through which the received pulses corresponding to one direction of transmission are applied to the corresponding amplifier, transmitting the amplified pulses corresponding to the other direction through one of the said paths, and blocking the said paths in turn in such manner that transmitted, pulses are prevented from reaching the said amplier, the arrangement being such that at least one of the said paths is always open to receive pulses.

The arrangement according to the invention enables pulses to be transmitted simultaneously in both directions through the repeater, and no particular relation is necessary between the pulse durations or repetition frequencies of the pulses transmitted in the two directions.

As will be pointed out, however, later, certain details of the repeater design will be determined by the maximum duration of and minimum separation between, any pulses which it is required to repeat.

There are two types of case which have to be considered, namely: (1) when the same communication medium connects the repeater to the next station in both directions, as for example in the case of a radio system using a single carrier frequency at the repeater; and (2) when different me'dia are used; for example when the repeater is connected to the adjacent stations by separate cables. In this case of course, each cable is used for transmitting pulses in both directions. In case (2), as will be pointed out later, the repeater may be slightly simplified.

The invention will be described with reference to the accompanying drawings in which:

Fig. l shows a block schematic circuit diagram of a two-way pulse repeater according to the present invention.

Figs. 2 and 3 respectively show two modications of Fig. 1;

Fig. 4 shows a detailed circuit of a repeater in accordance with Fig. 1;

Fig. 5 shows a modification of part of Fig. 4i

Fig. 6 shows a detailed circuit of an arrange-I ment in accordance with Fig. 3.

Fig. '7 shows a detailed circuit of an arrangement in accordance with a slightly modied form of Fig. 3; and

Fig. 8 shows a schematic circuit diagram of still another arrangement according to the invention.

Fig. 1 shows a block schematic circuit diagram of a relatively simple repeater according to the invention. It comprises two similar pulse ampliers indicated by the dotted outline; IE and IW used respectively for repeating pulses tothe adjacent stations to the east and west. Pulses from the west station arrive over a transmission circuit common to both directions, which is connected to terminal 2E, which is in turn connected to the amplifier IE` by two parallel paths respectively including delay networks 3E and 4E', and gate circuits 5E and 6E.

The amplifier IE comprises a blocking circuit 1E. followed by a receiving amplifier 8E. The output of the receiving amplifier is connected to the transmitting amplier 9E through a delay network IIlE. A switching pulse from the output of the delay network IUE is applied through a delay network IIE to control the blocking circuit 1E. This pulse should be at least as long as the amplified pulse transmitted by the amplifier l9E and a pulse shaping circuit IZE may be included if necessary to ensure that the switching pulse is long enough to give the blocking circuit time to operate.

The west repeating half of the repeater is identically arranged, and the corresponding elements are given the same designation numbers with the distinguishing letter W.

The outputs ofthe transmitting amplifiers 9E and 9W are connected respectively to the delay network 4W and 4E as shown, so that the amplied transmitted pulses are delivered through these delay networks and terminals 2W and 2E to the east and west stations, respectively. The switching pulses derived from the outputs of the amplifiers 8E and 8W are applied respectively 3 over conductors I3E and ISW to control the gate circuits W, 6W and 5E, 6E. For convenience, the input and output conductors of the amplifiers IE and IW will be designated ME, IEE and MW, I5W.

The delay networks 3E and 4E should each be designed to delay a pulse by the same amount, which Should be slightly greater than half the maximum duration of any pulse which will be transmitted from east to west. Likewise, the delay networks 3W and 4W should each delay a pulse Iby slightly more than half the maximum duration of any pulse which will be transmitted from west to east. The east and west networks do not need to be equal.

The networks I IE and I IW should each introduce a delay equal to, or slightly less than, that of networks 3E and 4W together, and 3W and 4E together respectively. The networks IUE and IDW may be situated anywhere in the corresponding path between terminals 2E and 2W, the preferredv position being shown. These networks are only necessary when the combined delay of networks 3E and 4W is less than the longest pulse transmitted from west to east, and

when the combined delay of networks 3W and 4E is less than the longest pulse transmitted from east to west. Each of the networks IUE and IUW should introduce a delay equal to the difference between the duration of the said longest pulse and the combined delay of the corresponding pair of networks 3 and 4 when this difference is positive. If the difference is Zero or negative, the corresponding network III may be omitted.

Considering rst transmission from west to east, the gate circuit 5E is normally closed to prevent any received pulses from reaching the amplier IE over the delay network 3E, but the gate circuit 6E normally open so that the rea ceived pulses reach the amplifier over the delay network 4E. However, when a transmitted pulse is delivered from the conductors I5W, at the same time a switching pulse is transmitted over conductor ISW and this pulse shuts the gate 6E and opens the gate 5E, so that the received pulses now reach the amplier IE over the delay network 3E. The transmitted pulse nds the gate 6E shut and so cannot reach the amplier IE. There is also aV path for the transmitted pulse through both the delay networks 4E and 3E, but since these together introduce a delay slightly greater than the maximum transmitted pulse, this pulse can never arrive at the gate 5E before this gate is shut again by the disappearance of the switching pulse applied over conductor I`-3W. Thus the transmitted pulse is prevented from reaching the amplier I E by either route; Since the gate SEopens at the same time as the gate 5E shuts, and vice versa, there will always be a path for the received pulses to the am'plier I-E. If the leading edge of the transmitted pulse arrives during the period of a received pulse, the rst position of the received pulse will travel over the delay network 4E and the second portion over the delay network 3E. These two portions will be properly reunited in the conductor I4E if the delay introduced by the networksE and 4E is the same.

When the amplified pulses are transmitted from the repeater in both directions over the same medium, the terminals 2E and 2W will be effectively connected together, and there is therefore a path for the pulses transmitted from east to west through the networks 4W and 3E to the input of the amplifier IE. This path is blocked by the blocking circuit 7E, operated by the pulses from the delay networks IIE. Since the delay introduced by this network is equal to or slightly less than, the combined delay of the networks 3E and 4W, the input to the amplier 8E is blocked when the pulse arrives over the above mentioned path. Further, since the combined delay of networks IUE and IIE is greater than the duration of the longest pulse transmitted from west to east, the pulse will be received before the receiver is blocked.

It will be understood that the pulses will be repeated from east to west in an exactly similar way.

If separate cables (or different radio carrier frequencies) are used for connection to the east and west stations, the blocking circuits 'IE and 'IW can be omitted, since the transmitted pulses cannot appear at the input of the amplier from which they were transmitted.

It should be pointed out that this simple arrangement according to the invention has the limitation that the interval between any two pulses cannot be less than the pulse duration. If this should happen, it can be seen that the rst transmitted Vpulse travelling through networks 4E and 3E may not have had time to disappear before the gate 5E is opened again by the switching pulse corresponding to the next transmitted pulse. This limitation may be avoided by another circuit to be described with reference to Fig. 3.

A modication of the arrangement of Fig. l is shown in Fig. 2. This modification only aiects the two paths by which the received pulses reach the corresponding amplifiers, and Fig. 2 shows only these paths for the easterly repeating direction, the modification for the other direction being similar.

In Fig. 2, the lower path includes a delay netn work IE and agate circuit ITE similar to 4E and 5E of Fig. l, the gate I'IE being normally open. The upper path includes a gate circuit I8E also normally open, followed by a delay network ISE. The gate circuits are controlled by the switching pulses from conductor IEW, which is connected directly to the gate circuit I'lE, ibut through a delay network 23E to the gate circuit ISE. The conductor IEW is connected between the elements IIEE and I'IE.

The delay networks ISE., ISE, and 2!E should all introduce the same delay, which should be slightly greater than the duration of the maximum pulse transmitted from conductor ISW.

In the absence of any transmitted pulses from conductor I5W, both gates are open and the received pulse travels to conductor I 4E over both paths. As soon as a transmitted pulse arrives, the gate I'IE will be shut by the corresponding switching' pulse arriving over conductor I3W. The gate I8E remains open however, and allows any received pulses to pass over the upper path. The switching pulse then shuts the gate I 8E, after being delayed by the network 2llE, just in time to block the transmitted pulse which has arrived at terminal 2E. Shortly after this time also the trailing edge of the switching pulse will have reached gate ITE and will open it again, so that the next received pulse (or the portion cut orf by the shutting of the gate I8E) will find the gate IIE open after passing through the delay network IE, provided (as in the case of Fig. l) that the transmitted pulse interval is not greater that the maximum pulse duration.

It will be noted that in this arrangement, the received pulse (or parts of it) may arrive at conductor I4E by either path, or by both paths simultaneously. The amplitude of this pulse may therefore vary, but as in time modulation communication systems, the pulse amplitude is immaterial, this will be no objection, and the pulses may be reduced to uniform amplitude by limiting action, for example, in the amplifier 8E' (Fig. 1).

Fig. 3 shows another modification of Fig. 1 which may be adapted for use with pulses of any desired .maximum duration and minimum spacing.

Let it be assumed that the maximum pulse duration is T, and that the minimum spacing between pulses is t. Then the circuit connecting the terminal 2E to the conductor I4E will comprise n+1 parallel paths, where n is the integer equal to or just greater than T/t. For illustration Fig. 3 shows a circuit for the case in which T=3t, so that 11:3. The four paths shown include four corresponding gate circuits 2IE, 22E, 23E and 24E all of which are normally open for the passage of received pulses. The lowest path comprises three similar delay networks 25E, 26E, and 21E' arranged in succession between the terminal 2E and the gate ZIE. The second path comprises the delay network 28E connecting the junction point of networks 25E and 26E with the gate 22E. The third and fourth paths comprise the delay networks 29E and 39E connected respectively between the junction point of networks 26E and 2'IE` and the gate 23E, and between the terminal 2E and the gate 24E.

The conductor 13W which conveys the switching pulse is connected to a series of delay networks SIE, 32E, and 33E. 'Ihe gate circuit ZIE is connected directly to the conductor I3W, and the gate circuits 22E, 23E` and 24E are connected respectively to the output sides of the delay networks 3IE, 32E and 33E'.

The conductor IEW conveying the transmitted pulses is connected between the delay networks 25E and the gate ZIE.

The delay networks 25E to 28E (inclusive) should be designed to introduce a delay of t/2; networks 29E, 3IE, 32E and 33E a delay of t, and network 3llE a delay of 3i/2.

It will be clear that in the absence of any transmitted pulses all gates are open and the received pulses reach conductor I4E from terminal 2E over all paths simultaneously. Since the total delay is the same over each path, the various components of each pulse combine together in a satisfactory way. As soon as a transmitted pulse arrives over conductor IEW, the corresponding switching pulse shuts the gate ZIE and then shuts the gates 22E, 23E, 24E after successive intervals of t, 2t and 5t.

The transmitted pulse also reaches these gates after the same intervals through successive pairs of the delay networks and nds all of them shut, so that the transmitted pulse cannot reach the conductor I4E.

However, since T=3t, at the time when the gate 24E is shut by the leading edge of the switching pulse the trailing edge will open the gate 2IE, thus ensuring that at least one of the four paths is always open for the received pulses. Thereafter the gates open in turn each for a period of t, the other three gates remaining shut.

In the above explanation it has been assumed that the shutting and opening of the gates is instantaneous. In practice slight adjustments will be necessary of the duration of the switching pulse and the delays introduced by the delay networks to allow for the operating times of the gate circuits.

It should be noted that the circuit will operate satisfactorily for any pulses for which the pulse duration is less than T and/or the pulse interval is greater than t. In this case more than one of the four paths may be open to receive pulses at the same time, but this is no objection, since as already explained, the pulse amplitudes may be made uniform by suitable limitation.

It will be understood, of course, that although Fig. 3 shows the modification only of the east transmitting side of Fig. 1, the west transmitting side will be modified in an exactly similar Way.

It will be clear that when n is greater than 3, additional paths may be provided and arranged according to the same plan. One or more additional delay networks will be connected between the terminal 2E and the delay network 21E', and the series of delay networks SIE to 33E will be extended in order to serve the necessary additional gate circuits and corresponding delay networks of the series 8E to 36E. The delay introduced by each additional one of the last mentioned delay networks should increase progressively by t/2.

Fig. 4 shows a detailed circuit diagram of a repeater in accordance with Fig. 1, Those parts of Fig. l which are directly identifiable in Fig. 4 have been given the same designation numbers. Only the east transmitting half of Fig. 4 will be described, since the west transmitting half is identical.

The normally shut and open gates 5E and 6E of Fig. 1 are represented respectively by two Valves 34E and 35E' arranged as cathode followers. The blocking circuit IE and receiving amplifier 8E are combined in the valve 36E and the transmitting amplifier is represented by the valve 31E; an additional amplier valve 38E not represented in Fig. 1 is inserted between the delay network IEE and the valve 31E.

Positive and negative terminals 39 and 40 are provided for the high tension source (not shown) for the valves, terminal 40 being grounded as shown. A terminal 4I for a negative bias source (also not shown) is provided.

The usual anode load resistance 42E, 43E and 44E, anode coupling condensers 45E, 46Ev and 41E and cathode bias networks 48E, 49E and 50E are provided respectively for the valves 36E, 31E and 38E. All these valves have the screen grids connected directly to terminal 39 and valves 31E and 38E have the suppressor grids connected to the cathodes. Grid leak resistances 5 IE and 52E are provided for the valevs 36E and 38E, and the anode condenser 45E is connected to ground through a resistance 52E.

A transformer 53E is provided for coupling the valves 38E and 31E. This transformer has a rst secondary winding 54E connecting the control grid of the valve 31E to ground, and a second secondary winding 55E connecting terminal 4I to the anode of the valve 34W in the other half of the repeater. A conductor 56E connects the control grid of the valve 31E to the suppressor grid of the valve 36E, through the delay network IIE.

This corresponds to the conductor IIE of Fig. 1, but no pulse shaper corresponding to IZE is necessary and is not shown in Fig. 4. The conductor 56E also extends to the control grid of the valve 35W in the other half of the circuit.

' catho I The valve 31E is provided with an output transformer iE the secondary winding of which is connected over conductor IE to the delay network HW in the other half of the circuit.

.The anode of the gate valve 35E is connected directly to terminal 39, and the suppressor grid Vis connected to the delay network 4E through a blocking condenser 58E and to ground through a high resistance 59E. The screen grid is polarised through a resistance 60E and is connected to the cathode through a condenser SIE. The control grid is connected to the control grid of Athe valve 37W in the other half of the circuit through conductor 56W. The cathode shares a cathode resistance 62E with the other gate valve 34E. The control grid of this Valve 34E is connected to the delay network 3E through a block- .ing condenser 53E and to ground through a high resistance (ME. The anode is connected to the secondary winding 55W of the transformer 53W in the other half of the circuit.

The cathodes of the valves 34E and 35E are connected by the input conductor IllE and through a blocking condenser 65E to the control grid of the valve 36E.

The delay networks 3E and 4E are provided with terminating resistances iE and 61E.

The gate valve 35E should be biassed so that it will normally accept and amplify the received pulses applied in positive sense through condenser 58E. However, transformer winding 513W supplies a switching pulse to the control grid of 'the valve 35E which coincides with the trans- -mitted pulse delivered over conductor The transformer should be poled so that this switching pulse is negative, and is of suilcient amplitude to cut onc the valve 35E. At the same time a duplicate but positive switching pulse applied from the winding 55W to energisethe valve' 34E, which then passes any received pulses, or portions thereof, to conductor IllE. As explained with reference to Fig. 1, the gate valve being shut, prevents the transmited pulse from reaching the conductor IE.

The negative bias applied to the windingiSW of the transformer-53W permits the opening of the gate valve 34E to be slightly delayed.

The valves SSEySSEand 3'iE act as conventional amplifiers except that the negative switching pulse generated by the winding of the transformer `53E is applied through the delay network HE to cut ori the valve 3BE on the suppressor grid, thus preventing the pulse tran."- mitted eastwords from re-entering the amplifier from terminal 2E.

The transformer 57E maybe poled that positive output pulses are delivered'to terminal 2W through the delay network 4W.

The delays specified above Vfor'the networks NBE and IIE have been chosenin Vorder to give time for the pulse to be completely received i .-efore the valve 33E is cut off during transmission of the pulse. If terminals 2E and Zware connected to separate communication media, then the delay network IGE can be omitted, and no blocking is required in'- thevalventtli so' that its suppressor grid can be omitted or connected to i instead of 15o conductor 58E.

The tra' iitting valve 31W by virtueof its bias, operates for a shorter time and slightly lafter the valve has been cut ofi by the negative pulce receivedy by its grid from transformer There is, however, a circuit from terminal 2E through the delay network 3E and through valve ylliE to valve 36E since this valve has a positive pulse applied to its anode from transformer 53W. Since delay networks and iE have a time delay equal to the duration of the switching pulse, the valve 34E will have ceased conducting'by the time the transmitted pulse arrives at its grid. Simultaneously valve 35E will be unblocked by the disappearance of the negative pulse from its grid. It will be seen, therefore, if terminals 2E and 2W are not connected to the same communication medium, that is, a separate path in either direction is available 'transmission through the repeater is continuous, If, however, the terminals 2E and 2W are connected to the same mediurn then through transmission is continuous except during the time each received vpulse is being re-transmitted, that is, there must always be a delay in the retransmission oi' pulses in the same direction equal to or slightly greater than the duration of the pulses.

It has been assumed that all the pulses are positive. The onlyalteration necessary for negative pulses is to reverse the primary windings of the transformers 53E, 5FE, 53W and 51W.

Details of the modication shown in Fig. 2 are given in 5. This figure replaces that part of the oi' iT-ig. which 1s to the left hand side of the blocking condenser 65E. The lower part of Fig. 4 to the right hand side of condenser 65W will be similarly modified.

I'he two gate circuits IiE and IEE of Fig. 2 are represented respectively by the two similarly arranged valves GEE and 59E having anode resistances 76E and i IE, anode blocking condensers and i317, suppressor grid resistances '14E and controi grid resistances ME and HE, suppresser grid blocking condensers 18E and 19E, control grid blocking condensers SBE and SIE, and cathode bias networks 82E and 83E, The anode condensers are connected to ground through resistances ME and 85E, and terminating resistances SEE and 8lE are provided respectively for the delay networks ISE and 20E.

The terminal 2E is connected directly to the control grid of the valve 63E. Both these valves should be biased so that they will normally pass the received pulses applied in positive sense at terminal 2E. The conductor I3W (which will be connected to the control grid of the valve 31W in Fig. 4) is connected directly to the suppressor grid of the valve 63E, and through the delay network ilE to the suppressor grid of the valve 69E. The negative switching pulse derives from the transformer 53W should be designed to cut off each of the valves SE and 69E when it arrives at the corresponding suppressor grid. It will be clear when Fig, 4 is modified according to Fig. 5, the secondary 'windings 55E and 55W of the transformers 53E and 53W and the bias source connected to terminal dl are not required. The anode of the valve 68E and the output of the delay networks ESE are connected to the conductor IiE as shown.

Fig. 6 shows details of the modication of Fig. 4 according to Fig. 3. Fig. 6 replaces the position of Fig. Li between the terminal 2E and the condenser E. The lower half of Fig. 4 between the terminal 2W and the condenser 65W may be modified similarly.

In Fig. 6,. the delay networks correspond exactly Vtc those of 3 and are given the same designation numbers, The gate circuits 2IE to 24E of Fig. 3 are represented in Fig. 6 by the valves 88E to BIE respectively. These valves are all similarly arranged and share a common anode resistance 92E and output blocking condenser 93E connected to conductor I4E. The valves are provided with cathode bias networks 94E to 91E and grid leak resistances 98E to IUIE.

The conductor I3W conveying the negative switching pulse from the control grid of the valve 31W (Fig. 4) is connected to the rst of the series of delay networks 3IE, 32E and 33E and the suppressor grids of the four valves are connected respectively directly to conductor I3W and to the outputs of these three delay networks. The conductor IEW conveying the transmitted pulse is connected to the control grid of the valve 88E. Terminating resistances I2E, I03E and IME are provided for the delay networks 25E, 26E and 21E.

The valves 88E to BIE should all be biased so that they will normally accept and amplify positive pulses received from terminal 2E over the corresponding paths and the negative switching pulse should be of suflicient amplitude to cut off any valve which it reaches. It should preferably be arranged so that the switching pulse occurs very slightly earlier and has a slightly greater duration than the corresponding transmitted pulse. It will be clear that this arrangement operates exactly as described with reference to Fig. 3. The circuit may be designed for larger values of T/ t than 3 by adding further similarly arranged valves with the necessary extra delay networks as described with reference to Fig. 3.

Fig. '7 shows a modication of Fig. 6 in which the anodes of the valves 88E to QIE are separates, and are provided with individual anode resistances IEIE to IEJBE. The three delay networks 28E, and 29E and 30E of Fig. 6 are omitted and, three corresponding networks IIJSE, IIOE, and IIIE are shown in Fig. 7 connecting the anodes of adjacent valves. The input conductor ME is connected through the blocking condenser 93E to the anode of the first valve 88E. All the delay networks in Fig. '7 should introduce the same delay t. It will be evident that the received pulses can reach the conductor I4 through four separate paths each having a delay equal to 315. The transmitted pulse arriving over conductor I5W will ind the valve 88E blocked by the switching pulse which arrives simultaneously over conductor ISW. On reaching valves 89E, 99E and 9 IEv after successive delays of t, 2t and 3i in networks 25E, ZSE-I-ZBE, and 25E-i-2GEi-1-21E, the transmitted pulse will find eachlof the three valves blocked by the switching pulse which reaches these valves after the same delays in networks SIE, 32E and 33E.

The arrangement of Fig. 7 is preferable to that of Fig. 6 since all the delay networks are equal, and moreover, in the case of the networks IOQE, IIUE and IIIE, the anode capacities of the valve may be employed to serve for certain of the delay networks components, or parts of them.

It should be pointed out the Fig. '7 will be in accordance with a slightly modied form of Fig. 3 in which the delay networks 28E, 29E and 30E are removed to positions in series with the conductors marked IIZE, IISE and II4E, respectively, in Fig. 3.

In all the embodiments of the invention which have been described so far it has been assumed that the transmitted and received pulses have the same sign. If it is arranged for them to have opposite signs, the circuits may be simplified.

The necessary conditions can be fullled in two ways:

(l) By arranging that all the pulses transmitted in one direction through a line of repeaters are positive, while all the pulses transmitted in the other direction are negative. This would require the two amplifiers in each repeater to handle pulses of opposite sign but neither amplifier should invert the pulses.

(2) By designing each amplier at each repeater to invert the pulses amplified thereby, and by arranging for the input, pulses arriving at any repeater from opposite directions to be of opposite sign. This will result in the pulses transmitted in any direction through a line of repeaters being alternately positive and negative in the successive sections between repeaters.

The methods of designing the ampliers to fulll any of these conditions are well known to those skilled in the art and do not need to be described.

Fig. 8 shows the terminal arrangements at one side of a repeater, and indicates the manner in which the portion to the left hand side of the condenser 65E of Fig. 4 would ibe inodied. The high tension conductor connected to terminal 39 of Fig. 4 is not needed in Fig. 8 and is therefore not shown.

In Fig. 8, the terminal 2E to which the received pulses are applied is connected to the first of a series of three delay networks II5E, IISE and II'IE connected in cascade. The input conductor IAE is connected to the output end of a second series of three delay networks IIBE, II9E and IZIlE also arranged in cascade. Four rectifiers IZIE, I22E, I23E and I24E connect the input and output sides of corresponding networks of the two series. These are all directed in the same direction and are shown with their anodes connected to the lower series of networks. The resistances I25E to IME represent terminations for the delay networks. The conductor conveying the transmitted pulses is connected to the output of the delay network II'IE. No switching pulses are required, so the conductor I3W and the winding 55W of the transformer 53W (Fig. 4) can be omitted.

Each delay network should be designed to introduce the same delay, namely t.

With the rectiers directedv in the manner :shown the received pulses should be positive and the transmitted pulses should be negative. When no transmitted pulse is present, the received pulse can pass through each of the four paths connecting terminal 2E to conductor HIE, respectively, including the four rectiers. Each of these paths has the same delay, namely, 3i.

As soon as a negative transmitted pulse arrives over conductor I5W it blocks the rectier I 24E, and so is prevented from reaching the conductor ME. This pulse blocks all the other rectiiiers in turn after delays of t, 2t and 3i respectively, but as before, so long as the number of paths is equal to or greater than l-l-T/t, the rst rectifier I24E will be unblocked by the time the transmitted pulse 4blocks the last rectier, so there is always at least one path open to the received pulses. It will be noted that although transmitted and received pulses may be simultaneously applied to the anode of any rectifier, the transmitted pulse will always have the greater amplitude, so that the rectier will be definitely blocked.

assenze It `will be evident that if the transmitted pulses are positive, and the received pulses are negative, the arrangement of Fig. 8 can be used if all the rectiiiers lZIE to l24E are reversed.

The rectiers may be diodes or crystal or metal rectiers of any suitable type.

When the arrangements are such that as in case (l) mentioned above, all the pulses used for transmission in one direction are positive and all those used for the other direction are negativa, it is evident that each repeater will require anr arrangement according to Fig. 8 at one end, and a similar arrangement With all the rectifiers reversed at the other end. In case (2) however, inl which each ampliiier is designed to invert all the pulses which it amplifies every alternate repeater" Will-require arrangements according to Fig. 8 atf both ends, While the remainder will require atY both ends the arrangement of Fig. 8 with all the rectiers reversed.

What is claimed is:

l. A two-way repeater for electric pulse trans mission systems employing a common transmission medium for two-directional transmission, comprising a pair of pulse amplifiers operative to amplify and retransmit pulses respectivelyA inv opposite directions over said transmission medium, a plurality of transmission paths connected from the input of each of said pulse ampli'ers to said common transmission medium, means for transmitting outgoing pulses from each of said ampliers over a circuit including a transmission path of the opposite amplifier, means for block ing said outgoing pulses from said respective amplier input and means for continually maintaining at least one of said transmission paths toV each ampliiier open for pulses incoming to said' ampliers.

2. A two-way repeater for electric pulse transmission systems, comprising two similar pulse amplifiers for amplifying and retransmitting pulses respectively in opposite directions, two' transmission circuits each operative to convey: input pulses for retransmission in one direction and also output pulses transmitted in the oppo-v site direction, a plurality of parallel conductive paths connecting each of said transmission cir-- cuits respectively to the input of said pulse arnpliiers, means for conveying retransmitted pulses from the output of either of said pulse amplifiers to respective of said transmission circuitsv over a circuit including a parallel path of said other amplier, means for preventing access ofV retransmitted pulses to said other amplifier over any of said `parallel paths and means for maintaining a circuit over at least one of said parallelY paths open for pulses incoming to each of saidJ ampliiiers over said transmission circuits.

3. A repeater according to claim 2 in which' each parallel path includes delay means connected therein such that received pulses reachth'e-input 0i the corresponding amplifier over any of said paths after a same delay, and in which each path also includes a gate circuitv Which is normally open for the passage of received pulses from said transmission circuits, and further comprising means for deriving a switching pulse from each of said amplifiers the duration of which is at least equal to that of a corresponding retransmitted pulse, and means for applying said switching pulses to close respective of said gate circuits in turn after corresponding delays such that any retransmitted pulse from said amplifiers iinds each gate closed in arrival thereat over said parallel paths.

4: Arepeater. according to` claim 3 in which" the switchingpulseis'applied directly to the gate circuit ofzthepath towhich the retransmittedv pulse isapplied, and to the other gate` circuits in turn after. successive delays increasing by a constant time t which is at least less than the minimum time interval vbetween any two retransmitted pulses.

5. A repeater according toclaim 4 in which the number. of the Said parallel paths is the integeriequal to (T-l-t) /t where T is the maximum duration .of any retransmitted pulse.

6*.- A repeater according to claim 5 in which (T-l-t) /t'isless than andcomprising two of the said parallel paths.

'7. A repeater according. to claim 6 in which` each gatev ircuitcomprises a therinionic valve normally operative to transmit pulses applied thereto; and inWhich means is provided for applying said switching pulses in negative sense to a grid electrode the said valve in order tol hloci'it;

8. A repeater according' to claim 2 including' two' parallel f paths .connecting each transmission' circuit te the corresponding ampliiiercver eitherpath after a predetermined delay, in which one oithepaths inciudes a rst gate circuit normally open for the passage of received pulses, and the other' includes a second gateV circuit normally closed forrcfeived pulses,` comprising means for deri sa hing pulses from the said other amplifier the duration of which is at least equal to that of a corresponding retransmitted pulse, andmeans for applying the switching pulses to close said lirst gate circuit and to open said sccond gate circuit.

D. A repeater according to claim 8 in which the iirst gate circuit comprises a thcrmionic valve arranged normally to transmit pulses applied thereto, and in which means is provided for applying a switching pulse in negative sense to a grid electrode of the said valve in order to block it.

10. A repeater according tol claim 9 in which the second gate circuit comprises a thermionic valve, and which means is provided for applying a switching pulse in positive sense to the anode thereof for providing the operating potential.

ll. A repeater according to claim 2 in which each of the said parallel paths includes a gating valve comprising means for applying pulses receivedover said transmission circuits to the said gating valves over respective delay means all introducing the same delay, means for connecting theA outputs of all the gating valves directly to the said corresponding amplier, and means for applying a switching pulse in negative sense to a grid electrode of the gating valve in the path to which the transmitted pulses are applied, and to a .grid electrode in each of the remaining gating valves after progressively increasing delay.

l2. A repeater according to claim 2 in which each of the said paths includes a gating valve, comprising means for applying pulses received over said transmission circuits to the nrst gating valve in the path to which the transmitted pulses are applied after a given delay, and to the other gating valves after progressively decreasing delay, means for connecting the outputs of all the gating valves to the said corresponding amplier after progressively increasing delays such that the ltotal delay obtained in reaching the said corresponding amplifier is constant, and means for applying switching pulses directly to a grid electrode of the first gating Valve, and to a grid elec- 13 trode in each of the remaining valves after progressively increasing delay.

13. A repeater according to claim 1 in which the said plurality of transmission paths comprises two series each consisting of the same number of delay devices arranged in cascade, corresponding devices of each series introducing the same delay, a plurality of rectiers, one which connects the input of each delay network of one series to the input of the corresponding delay network of the other series, means for supplying `pulses received over said common transmission medium of one sign to the input of one of the said series and transmitted pulses of the oppo- 14 site sign to the output thereof, and means for connecting the output of the other series to the said amplier connected to said transmission paths,

CHARLES THOMAS SCULLY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Deloraine et a1. Oct. 28, 1947 

